The present invention is directed generally to relay circuits and more particularly to a novel power-saving relay circuit and to a method for reducing power consumption of a relay circuit.
A relay circuit generally comprises a relay coil for moving or throwing one or more related movable contactor elements or switches between pairs of fixed contacts or terminals. In this regard, a typical relay may include a number of such switches or movable contactors. Each of these movable contactors is responsive to energization of a relay coil for breaking electrical contact with a first or normal closed contact or terminal and making electrical contact with a second or normally open fixed contact or terminal. Thereafer, continued energization of the relay coil holds the respective movable contactors in electrical engagement with the associated second or normally open fixed contacts or terminals.
In many applications, for example in portable battery-powered apparatus, it is desirable to minimize the power consumption of one or more such relays. Most such relays are designed to draw a given current and hence consume a given amount of power to effect the initial movement of the movable contactors or switches between the fixed contacts or terminals. However, after making of the second or normally open contacts, most such relays exhibit from 20 to 50 percent less current consumption and hence correspondingly less power consumption to hold the contactors in engagement with the second or normally open contacts or terminals. Accordingly, most relays consume more power than is necessary, since the associated power circuit usually provides a fixed current through the relay coil when energized.
In view of the foregoing, provision of an additional current limiting resistor in the power circuit to the relay coil would not be appropriate, since this would reduce the current draw and hence power of the coil at all times. This might provide insufficient power to cause the initial breaking of engagement and movement of the movable contactors. However, if the relay coil and a current limiting resistor are placed in circuit with one of the sets of normally open contacts and the associated movable contactor, the relay coil will be without power, and hence unable to operate the relay, during the time when the movable contactor is moving between the normally closed and normally open contacts.